In a future optical network, for example, processes of branch insertion or switching of signal light need to be performed in a device installed in a place separated from repeater optical nodes or terminal devices, while using as a base a conventional optical communication system. In the case of terminal devices, for example, the above-described processes are performed by using a method for converting electrical signals as data into optical signals by light modulators. However, in the repeater optical node of future optical network, the conversion from electrical signals to optical signals is used as in the above-described terminal device. In such a case, transmitted optical signals are converted into electrical signals once, and the signals are electrically processed (waveform shaping). Then, the electrical signals need to be converted into optical signals again. In this case, a configuration becomes complicated and loss generated during opto-electronic conversion is compensated, and as a result, large power is needed.
As a technique related to the above, known is a technique of realizing a high-speed switching by optical signals in high switching efficiency over a sufficiently wide wavelength range (see, for example, Japanese Laid-open Patent Publication No. 2006-184851). Further, known is a technique of efficiently shaping a waveform of a deteriorated optical signal (see, for example, Japanese Laid-open Patent Publication No. 2007-264319). Further, known are an apparatus and system for optical phase conjugation and wavelength conversion usable as a converter that is wide in a conversion band and has no dependence on polarization (see, for example, Japanese Patent No. 3566096).
As described above, in a repeater optical node of an optical network, when data of optical signals is moved to another light wave in a process of branch insertion or switching of signal light, since opto-electronic conversion is performed once, large power loss is generated.